1. Field of the Invention
The invention relates to vehicle transmissions, i.e. the series of members transmitting the rotational movement of the engine to the wheels of the vehicle, which members comprise a gear-box, a rear axle and a double cardan shaft for transferring the torque from the gear-box to the rear axle while allowing relative transverse movements thereof.
It relates more particularly, among these transmissions, to those equipped with an electric eddy current retarder exerting a braking torque thereon at desired times, the retarder being mounted directly on the casing of the gear-box of the vehicle and comprising an annular inductive stator cantilevered on the casing considered by means of an appropriate frame and a rotor comprising two induced ferromagnetic material discs which surround the stator and are both supported by a part itself cantilevered on a stub shaft inside the casing, each disc being fixed for this purpose, by means of a ring of arms forming ventilation fins, to a ring which is in its turn fixed to said part.
2. Description of the Prior Art
In known embodiments of the transmissions of the kind in question, the part on which the two rings are mounted is generally a special insert plate which is fixed both to a "gear-box flange" extending radially outwardly an end of a splined socket introduced into a "nose" of the casing of the gear-box, which socket is fixed on a stub shaft inside this nose and, on the axial side opposite this stub shaft, to an end flange of the contiguous cardan joint.
It should in fact be noted that it is not possible in practice to fit the rotor crowns directly on the gearbox flange, for the crown disposed on the gear-box side would then have to be mounted before the flange is positioned on the gear-box.
Now, such positioning is provided by tight fitting together of complementary splines formed respectively on the stub shaft inside the gear-box and the socket which the gear-box flange extends such force fitting only being able to be carried out with the flange not loaded.
It should be noted in this respect that, in the assembly according to patent FR-2 039 556, the flange on which the rotor crowns are mounted is not comparable with the above defined "gear-box flange": in fact, in this 10 prior assembly, the socket which is extended by the flange is not introduced into a "nose" of the casing, but in a sleeve forming part of the stator of the retarder, to which stator the rotor is pre-assembled in the factory with interpositioning of a bearing.
When such a retarder is mounted on the "nose" of a gear-box, the axial length of the socket is added to that of the "nose", which results in a great length between the gear-box and the flange, which length is incompatible with the objects pursued by the present invention which will be explained hereafter.
In so far as the above mentioned special insert plate is concerned, it must have a certain thickness since it must be able to transmit the whole of the drive torque of the vehicle from the cardan to the gear-box flange.
Thus, it has the double drawback of relatively high weight and axial dimension.
The last drawback may be serious in the case of very short transmissions, i.e. in which a limited space is available between the output of the gear-box and the input of the rear axle.
This is in particular the case for certain modern buses or coaches with rear engine, in which the overall length of the engine/gear-box assembly and that of the rear axle, particularly of hypoid type, increase without the respective positions of these members being modified.
In such a case, it may be vital to reduce the extension of the transmission due to the fitting of an electric retarder of the above kind thereon by a few centimeters, the possibility of adopting such a retarder being sometimes directly related to such a reduction.